A long term evolution (LTE) radio access technology (RAT) may be deployed on an unlicensed frequency spectrum, which is also known as licensed assisted access (LAA) or LTE unlicensed (LTE-U). One of possible deployment scenarios for the LAA is to deploy LAA carriers as a part of carrier aggregations, where an LAA carrier is aggregated with another carrier on a licensed frequency spectrum. In a conventional scheme, a carrier on a licensed frequency spectrum is assigned as a primary cell (PCell) and a carrier on an unlicensed frequency spectrum is assigned as a secondary cell (SCell) for a UE. Since there may be other RATs operating on the same unlicensed frequency spectrum as the LAA carrier, there is a need to enable co-existence of other RAT with LAA on an unlicensed frequency spectrum without undesirable interference between heterogeneous RATs.